Noise levels in neonatal intensive care units (NICUs) may have serious adverse effects on high risk infants by increasing apneic, bradycardic, or desaturation episodes; sleep disturbances; mechanical ventilation; hospital stay; poor growth; hearing deficits; or long-term developmental problems. Excessive noise may be particularly hazardous for extremely low birth weight (ELBW) infants (<=1000 g) who now survive in large numbers following months of NICU care and who account for a disproportionate number of impaired children. Methodologically strong studies are needed to assess noise exposure in NICUs and its effects on ELBW infants. Our specific aims are: 1. To conduct a longitudinal study to characterize the sound environment experienced by ELBW infants in a contemporary NICU. Microphones secured near the head of ELBW infants will be used to make recordings throughout the 1 week and for 24-hour periods each week thereafter (approximately 8 total weeks) until 35 weeks postmenstrual age (when noise exposure is usually substantially reduced and some infants are discharged home). 2. To identify sound characteristics in NICUs that disrupt sleep or increase episodes of apnea, bradycardia, or desaturation in ELBW infants. A random sample of ELBW infants (n=30) will be evaluated to relate the levels and spectral and temporal characteristics of sounds to arousals from sleep and episodes of apnea, bradycardia, and desaturation. Hearing and arousal thresholds will also be determined. 3. To conduct a randomized controlled trial assessing the effects of a simple and inexpensive method to reduce NICU noise exposure (silicone earplugs) on the outcomes of EBLW infants through 2 years adjusted age. The earplugs to be used reduce sound exposure by 20 db and are well tolerated by the infant and accepted by NICU staff. They will be removed to allow exposure to human voices during parental visits and during breast or bottle feedings. Based partly on prior studies, the intervention is hypothesized to increase mean weight gain by >=2 g/d above that of controls and protect the development of auditory evoked responses, reducing the latency of wave 5 by >=0.25 ms below that of controls at 35 weeks postmenstrual age (alpha=0.05; power=0.80). Apneic, bradycardic, and desaturation episodes; arousal from sleep; head growth; otoacoustic emissions; duration of mechanical ventilation, oxygen administration, and hospital stay; and growth, hearing, and development at 2-years will also be evaluated. Resources include a large population of ELBW infants, a newly constructed NICU, a clinical staff highly supportive of clinical research, and a strong follow-up program with low attrition rates and reliable assessments. The research team consists of respected investigators skilled in assessing NICU noise, evaluating infant responses, and performing randomized trials addressing important short and long term outcomes of ELBW infants.